How to get the maximum output voltage from the MAX2606 VCO

[dumindu89]

According to the datasheet of MAX2606, Absolute maximum rating for OUT+, OUT- to GND -0.3V to (Vcc+0.6V). And Vout (p-p) (differential) = 2x1mA[(1kΩxRload)/(1kΩ+Rload) I implemented the following circuit (both C2 and C3 are 2.2nF and other values are same as in the diagram) and get the single ended output and measured using the oscilloscope. **broken link removed** Unfortunately the output peak to peak voltage is just 300mV. (Vcc = 4.5V) Why I can't get at output peak to peak voltage least up to 1/2Vcc ? Please help me, I want to input the output of this to a 74F14 schmmit trigger IC. Any suggestions please?

 

[keith1200rs]

Absolute maximum ratings are what the chip will withstand without blowing up - it is not a performance statement. The chip will supply a maximum of -8dBm differential. I don't know what that is in V but it is a lot less than you want, I suspect (and even less if you use it single ended).

Keith

 

[jiripolivka]

Absolute maximum ratings are what the chip will withstand without blowing up - it is not a performance statement. The chip will supply a maximum of -8dBm differential. I don't know what that is in V but it is a lot less than you want, I suspect (and even less if you use it single ended).

Keith

The easiest way is to add an amplifier. If you only need a TTL type output, use a Schmitt trigger or a TTL-output comparator. Squeezing more than a specified output often kills a good device.

- - - Updated - - -

If you only need a narrow-band output, use a suitable transformer with its primary connected to OUT+ and OUT- via the capacitor shown, the secondary of it connected from GND to OUT. This way yo can get almost 2xVcc to a high-impedance load.

 

[dumindu89]

Absolute maximum ratings are what the chip will withstand without blowing up - it is not a performance statement. The chip will supply a maximum of -8dBm differential. I don't know what that is in V but it is a lot less than you want, I suspect (and even less if you use it single ended).

Keith

What do you mean by V? output voltage? It should be at least 2V (or more).
What should I use for the second load if I use differential mode? A resistor?

The easiest way is to add an amplifier. If you only need a TTL type output, use a Schmitt trigger or a TTL-output comparator. Squeezing more than a specified output often kills a good device.

- - - Updated - - -

If you only need a narrow-band output, use a suitable transformer with its primary connected to OUT+ and OUT- via the capacitor shown, the secondary of it connected from GND to OUT. This way yo can get almost 2xVcc to a high-impedance load.

Yeah. I tried to add an transistor amplifier (2N2222) but since it's fT is around 250 MHz, I couldn't get a amplified voltage (@ 100 MHz and Vcc of the amplifer circuit is 5V) to input to 74F14 Schmitt trigger. However, I didn't try it for differential mode. I ordered a transistor with higher fT (9 GHz) and I have to wait until it delivered to me. probably until next week.
But I need a much quicker solution for this.

Can you explain more about this?

If you only need a narrow-band output, use a suitable transformer with its primary connected to OUT+ and OUT- via the capacitor shown, the secondary of it connected from GND to OUT. This way yo can get almost 2xVcc to a high-impedance load.

If I changed the C2 or C3 capacitor values, can I see a better output voltage than this? (R1 & R2 should be connected each other and also C2, though they are not connected in schematic I posted in the first posted, and should be corrected as follows)
**broken link removed**

 

[keith1200rs]

-8dBm is 89mV according to my calculations.

If you want a logic output I would look for a high speed comparator and AC couple to it, with some biasing resistors.

Keith

 

[jiripolivka]

What do you mean by V? output voltage? It should be at least 2V (or more).
What should I use for the second load if I use differential mode? A resistor?




Yeah. I tried to add an transistor amplifier (2N2222) but since it's fT is around 250 MHz, I couldn't get a amplified voltage (@ 100 MHz and Vcc of the amplifer circuit is 5V) to input to 74F14 Schmitt trigger. However, I didn't try it for differential mode. I ordered a transistor with higher fT (9 GHz) and I have to wait until it delivered to me. probably until next week.
But I need a much quicker solution for this.

Can you explain more about this?

If I changed the C2 or C3 capacitor values, can I see a better output voltage than this? (R1 & R2 should be connected each other and also C2, though they are not connected in schematic I posted in the first posted, and should be corrected as follows)
**broken link removed**

You have never indicated what is your frequency and load impedance. The capacitors C2 and C3 are good for > 10 MHz. A 2N2222 transistor should be a good RF amplifier for up to >100 MHz. Use it at 12V DC and use AC coupling to the following TTL load.